9.1-STABLE zfsloader failure

[Roberto de Iriarte]

Yesterday, i updated /usr/src and proceeded to rebuild world + kernel as 
usual on a zfs root install (single disk)

After installing the machine refused to boot with the following error

ZFS: can't find pool by guid

After booting from CD, i first tried to reinstall gptzfsboot, which 
worked but did not solve the problem

I had to revert to the (thankfully existing!) zfsloader.old in order to 
be able to boot

My disk layout is as follows

Geom name: ada0
modified: false
state: OK
fwheads: 16
fwsectors: 63
last: 625142414
first: 34
entries: 128
scheme: GPT
Providers:
1. Name: ada0p1
    Mediasize: 65536 (64k)
    Sectorsize: 512
    Stripesize: 0
    Stripeoffset: 17408
    Mode: r0w0e0
    rawuuid: 400762ff-df42-11e2-95a9-001cb3c56dfb
    rawtype: 83bd6b9d-7f41-11dc-be0b-001560b84f0f
    label: (null)
    length: 65536
    offset: 17408
    type: freebsd-boot
    index: 1
    end: 161
    start: 34
2. Name: ada0p2
    Mediasize: 8589934592 (8.0G)
    Sectorsize: 512
    Stripesize: 0
    Stripeoffset: 86016
    Mode: r1w1e1
    rawuuid: 517ea784-df42-11e2-95a9-001cb3c56dfb
    rawtype: 516e7cb5-6ecf-11d6-8ff8-00022d09712b
    label: swap0
    length: 8589934592
    offset: 86016
    type: freebsd-swap
    index: 2
    end: 16777383
    start: 168
3. Name: ada0p3
    Mediasize: 311482892288 (290G)
    Sectorsize: 512
    Stripesize: 0
    Stripeoffset: 86016
    Mode: r1w1e2
    rawuuid: 5b9f74d2-df42-11e2-95a9-001cb3c56dfb
    rawtype: 516e7cba-6ecf-11d6-8ff8-00022d09712b
    label: disk0
    length: 311482892288
    offset: 8590020608
    type: freebsd-zfs
    index: 3
    end: 625142407
    start: 16777384
Consumers:
1. Name: ada0
    Mediasize: 320072933376 (298G)
    Sectorsize: 512
    Mode: r2w2e5

The new kernel works ok so far

FreeBSD mbp 9.1-STABLE FreeBSD 9.1-STABLE #0 r252531: Wed Jul  3 
00:14:13 CLT 2013     root at mbp:/usr/obj/usr/src/sys/GENERIC  amd64

Is there anything i can do to help debug the problem?

Best regards,
Roberto